This thesis deals with some of the theoretical and practical aspects relating to the conversion gain and noise performance of mixers employing dual-gate field effect transistors (DGFET'S) . To start with, the role of mixers in the context of radio conununication receivers is highlighted and the most relevant mixer properties are explained. Solid state mixing devices and their circuits are then discussed with special emphasis on the DGFET.This includes a survey and explanation of mixing devices ,planar transmission lines and circuit components for the practical design of mixers. Chapter 3 then deals with the mixer signal analysis as well as accuracy considerations. A more detailed treatment of the DGFET in terms of structure and dc model is given in the subsequent chapter. Problems associated with the choice of an FET model are referred to as well as the use of MATLAB for computationa: purposes. This is followed in the next two chapters with the development and analysis of the large signal equivalent circuit of tr.{· DGFET,and a treatment of noise and its measurement as associated with mixers. The design, practical implementation and measurement of the properties of DGFET mixers is covered in chapter 7. This is followed in Chapter 8 by an overall discussion of results, possible future work and conclusions. A new FET model is proposed that enables the dc characteristics to be simulated more closely than in previous models, particularly at low drain voltages. Furthermore, the representation of the noise by a frequency independent drain current generator and an input noise conductance enabled a single set of measurements to simulate the noise behaviour of the device as an amplifier or a mixer. Practical investigations using an NEe device type NE 41137 gave a maximum stable conversion gain in the frequency range O.SGHz to 3.0GHz of 4dB with a minimum noise figure 8.SdB.